EN
Behavioural sensitization is an enhancement of certain drug-induced effects which develops following repeated, intermittent exposure to opioids and psychoactive drugs. The sensitization can be measured in various animal models, e.g. conditioned place preference paradigm. In the present studies we undertook to investigate an involvement of adenosine receptor agonists in expression of sensitization to morphine-induced rewarding effects in rats. Three, intraperitoneal (i.p.) injections of morphine (5.0 mg/kg) induced conditioned place preference. Five days later, in animals with prior history of morphine administration, ineffective dose of morphine (0.75 mg/kg i.p.) was administered. That dose was able to induce a signifi cant intensifi cation of morphine response in conditioned place preference paradigm. It showed that morphine-induced sensitization to rewarding effects had been developed. To determine the effects of adenosine receptor agonists on expression of sensitization, selective and non-selective drugs were administered 15 min before the last injection of morphine. We showed that all adenosine drugs were able to attenuate the expression of morphine sensitization and the strongest effects were produced by selective (A1) and non-selective (A1 and A2A) adenosine receptor agonists. We conclude that adenosine agonists may play an important role in drugseeking behaviour underlying the development of addiction.